Is it true that difficult access to silanol can be a problem for obtaining a good peak shape?
This is probably not a correct statement. A sterical problem cannot be observed in electrostatic interaction because this is long force interaction. Oppositely charged ions interact as far as a few hundred angstroms in an aqueous salt solution. This makes ion-exclusion chromatography possible. The real reason for unwanted silanol interaction of basic and specially basic hydrophobic analytes is that acidic silanols can have some degree of ionization, even at a pH of the MP below 2, because they are shielded from the MP by the RP layer. The analytes, while within this layer, can interact with silanol electrostatically because the local pH within the stationary phase layer is not the same as in the MP. Solvated H+ ions have much more affinity to an aqueous MP than to a hydrophobic RP, and as result the pHs of the MP and RP are very different.
